In the manufacture of semiconductor devices and other products, ion implantation is used to dope semiconductor wafers, display panels, or other workpieces with impurities. Ion implanters or ion implantation systems treat a workpiece with an ion beam, to produce n or p-type doped regions or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material, wherein implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n type extrinsic material wafers, and implanting materials such as boron, gallium or indium creates p type extrinsic material portions in a semiconductor wafer.
FIG. 1A illustrates an exemplary ion implantation system 10 having a terminal 12, a beamline assembly 14, and an end station 16. The terminal 12 includes an ion source 20 powered by a high voltage power supply 22 that produces and directs an ion beam 24 to the beamline assembly 14. The beamline assembly 14 consists of a beamguide 32 and a mass analyzer 26 in which a dipole magnetic field is established to pass only ions of appropriate charge-to-mass ratio through a resolving aperture 34 at an exit end of the beamguide 32 to a workpiece 30 (e.g., a semiconductor wafer, display panel, etc.) in the end station 16. The ion source 20 generates charged ions that are extracted from the source 20 and formed into the ion beam 24, which is directed along a beam path in the beamline assembly 14 to the end station 16. The ion implantation system 10 may include beam forming and shaping structures extending between the ion source 20 and the end station 16, which maintain the ion beam 24 and bound an elongated interior cavity or passageway through which the beam 24 is transported to one or more workpieces 30 supported in the end station 16. The ion beam transport passageway is typically evacuated to reduce the probability of ions being deflected from the beam path through collisions with air molecules.
Low energy implanters are typically designed to provide ion beams of a few thousand electron volts (keV) up to around 80-100 keV, whereas high energy implanters can employ linear acceleration (linac) apparatus (not shown) between the mass analyzer 26 and the end station 16, so as to accelerate the mass analyzed beam 24 to higher energies, typically several hundred keV, wherein DC acceleration is also possible. High energy ion implantation is commonly employed for deeper implants in the workpiece 30. Conversely, high current, low energy ion beams 24 are typically employed for high dose, shallow depth ion implantation, in which case the lower energy of the ions commonly causes difficulties in maintaining convergence of the ion beam 24.
In the manufacture of integrated circuit devices and other products, it is desirable to uniformly implant the dopant species across the entire workpiece 30. Different forms of end stations 16 are found in conventional implanters. “Batch” type end stations can simultaneously support multiple workpieces 30 on a rotating support structure, wherein the workpieces 30 are rotated through the path of the ion beam until all the workpieces 30 are completely implanted. A “serial” type end station, on the other hand, supports a single workpiece 30 along the beam path for implantation, wherein multiple workpieces 30 are implanted one at a time in serial fashion, with each workpiece 30 being completely implanted before implantation of the next workpiece 30 begins.
The implantation system 10 of FIG. 1A includes a serial end station 16, wherein the beamline assembly 14 includes a lateral scanner 36 that receives the ion beam 24 having a relatively narrow profile (e.g., a “pencil” beam), and scans the beam 24 back and forth in the X direction to spread the beam 24 out into an elongated “ribbon” profile, having an effective X direction width that is at least as wide as the workpiece 30. The ribbon beam 24 is then passed through a parallelizer 38 that directs the ribbon beam toward the workpiece 30 generally parallel to the Z direction (e.g., generally perpendicular to the workpiece surface). Although the terminal 12, the beamline assembly 14, and the end station 16 are illustrated as separate or discrete systems, one or more of these may be combined or components thereof may be shared, for example, wherein the terminal 12 may extend to include or encompass the beamguide 32, and other beamline assembly components through the parallelizer 38.
Referring also to FIGS. 1B-1E, the scanner 36 is illustrated in FIG. 1B, having a pair of scan plates or electrodes 36a and 36b on either lateral side of the beam path, and a voltage source 50 that provides alternating voltages to the electrodes 36a and 36b, as illustrated in a waveform diagram 60 in FIG. 1C. The time-varying voltage potential between the scan electrodes 36a and 36b creates a time varying electric field across the beam path therebetween, by which the beam 24 is bent or deflected (e.g., scanned) along a scan direction (e.g., the X direction in FIGS. 1A, 1B, and 1C-1J). When the scanner electric field is in the direction from the electrode 36a to the electrode 36b (e.g., the potential of electrode 36a is more positive than the potential of electrode 36b, such as at times “a” and “c” in FIG. 1C), the positively charged ions of the beam 24 are subjected to a lateral force in the negative X direction (e.g., toward the electrode 36b). When the electrodes 36a and 36b are at the same potential (e.g., zero electric field in the scanner 36, such as at time “e” in FIG. 1C), the beam 24 passes through the scanner 35 unmodified. When the field is in the direction from the electrode 36b to the electrode 36a (e.g., times “g” and “i” in FIG. 1C), the positively charged ions of the beam 24 are subjected to a lateral force in the positive X direction (e.g., toward the electrode 36a).
FIG. 1B shows the scanned beam 24 deflection as it passes through the scanner 36 at several exemplary discrete points in time during scanning prior to entering the parallelizer 38 and FIG. 1D illustrates the beam 24 impacting the workpiece 30 at the corresponding times indicated in FIG. 1C. The scanned and parallelized ion beam 24a in FIG. 1D corresponds to the applied electrode voltages at the time “a” in FIG. 1C, and subsequently, the beam 24b-24i is illustrated in FIG. 1D for scan voltages at corresponding times “c”, “e”, “g”, and “i” of FIG. 1C for a single generally horizontal scan across the workpiece 30 in the X direction. FIG. 1E illustrates a simplified scanning of the beam 24 across the workpiece 30, wherein mechanical actuation (not shown) translates the workpiece 30 in the positive Y direction during X direction scanning by the scanner 36, whereby the beam 24 is imparted on the entire exposed surface of the workpiece 30.
Prior to scanning in the scanner 36, the ion beam 24 typically has a width and height profile of non-zero X and Y dimensions, respectively, and may not be truly symmetrical (e.g., may have a non-unity aspect ratio of Y/X dimensions), wherein one or both of the X and Y dimensions of the beam vary during transport. As the beam 24 is transported along the beam path toward the workpiece 30, the beam 24 encounters various electric and/or magnetic fields and devices that may alter the beam width and/or height. In addition, space charge effects, including mutual repulsion of positively charged beam ions, tend to diverge the beam (e.g., increased X and Y dimensions), absent countermeasures.
With respect to the beam 24 that is actually provided to the workpiece, the geometry and operating voltages of the scanner 36 provide certain focusing properties with respect to the ion beam 24. Even assuming a perfectly symmetrical beam 24 (e.g., a pencil beam) entering the scanner 36, if the scanner focusing properties are such that the focal distance of the scanner 36 and the parallelizer 38 provide a focal distance equal to the distance from the effective vertex of the scanner 36 to the workpiece 30 at the outermost scanned edges in the X direction, the bending of the beam 24 by the scanner 36 changes the beam focusing, wherein the incident beam typically is focused only at the lateral edges in the X direction (e.g., 24a and 24i inn FIG. 1D), and will be unfocused (e.g., wider or more divergent) in the X dimension for points between the lateral edges (e.g., 24c, 24e, and 24g in FIG. 1D).
FIGS. 1F-1J illustrate the incident beam 24 corresponding to the scanned instances 24a, 24c, 24e, 24g, and 24i, respectively. As the beam 24 is scanned across the wafer 30 in the X direction, the X direction focusing of the scanner 36 varies, leading to increased lateral defocusing of the incident beam 24 as it moves toward the center, and then improved focusing as the beam 24 again reaches the other lateral edge. In this case, the focal length of the scanner 36 is essentially set to the distance the beam 24 travels from the vertex of the scanner 36 to either of the outermost edges in the X direction (e.g., beams 24a and 24i). In this case, for no scanning, the beam 24e proceeds directly to the center of the workpiece 30, at which the incident beam 24e has an X direction width WC, as shown in FIG. 1H. As the beam 24 is scanned laterally in either direction away from the center, however, the time varying focusing properties of the scanner 36 lead to stronger and stronger lateral focusing of the incident beam. For instance, at the outermost edges of the workpiece 30, the incident beam 24a in FIG. 1F has a first left side width WL1, and on the right side, the incident beam 24i in FIG. 1J has a first right side width WR1. FIGS. 1G and 1I illustrate two intermediate beams 24c and 24g having incident beam widths WL2 and WR2, respectively, showing X direction focal variation between the edges and the center of the workpiece 30.
In order to counteract the focal variation of the scanner 36 along the scan direction, conventional ion implantation system designs often provide a fairly long distance between the scanner 36 and the wafer 30, whereby the dimensional variation of the scan direction beam dimension (e.g., X dimension) is small. However, as implantation uniformity specifications are increased for ion implanters, such focal variation becomes less and less tolerable. Furthermore, for high current, low energy ion beams 24, long drift distances between the scanner 36 and the workpiece 30 are more prone to beam blowup due to mutual repulsion of the beam ions. Therefore, there is a continuing need for improved ion implantation systems and scanning systems by which the time varying focal properties of beam scanning apparatus can be controlled or improved.